This invention relates to a steering sensor installed in an existing automotive vehicle for the purpose of sensing steering angle.
In order to control the operation of an automotive vehicle, the ability to sense steering angle is not often a necessity in conventional applications. Therefore, rather than mounting a steering sensor in all models of automotive vehicles, the usual practice is not to equip ordinary vehicles with such a sensor. Accordingly, when it is desired to fit an automotive vehicle with a steering sensor, these circumstances make it necessary to install the sensor in advance, namely during the manufacturing phase, as far as the prior art is concerned. Consequently, the conventional steering sensor mounted on a vehicle is of an already fabricated type, with a light-transmissive photosensor being employed as this sensor.
In recent years, however, cases in which steering angle information is utilized in order to achieve various types of control in automotive vehicles have increased. For example, such information is utilized in controlling four-wheel drive vehicles and in navigation systems for guiding a vehicle to a certain destination.
More specifically, in order avoid a tight-corner braking phenomenon or slipping phenomenon in a four-wheel drive vehicle, it is necessary to sense the occurrence of these phenomena from steering angle and vehicle velocity and control a rotational speed differential mechanism for the front and rear wheels of the vehicle. Furthermore, in an arrangement where the condition of the road surface ahead of the vehicle is sensed and the vehicle is controlled based on the road surface condition in order to stabilize the maneuverability of a four-wheel drive vehicle, it is necessary that the condition of the road surface ahead of the vehicle be accurately grasped at all times by sensing the steering angle, and that this information be properly exploited.
In a configuration where a vehicle is equipped with a navigation system for automatically guiding the driver to a specific destination, a steering sensor is required as means for checking the route travelled. For example, when steering angle is sensed by a steering sensor, intersections can be recognized, and a specific intersection along the route can be verified by performing a calculation using intersection information and distance travelled, thereby making it possible to enhance the reliability of the navigation system. Accordingly, in order to equip an existing automotive vehicle with a navigation system, there is need of a steering sensor with which such a vehicle can be retrofitted in a simple manner.
However, the conventional steering sensor has a sensing section of a light-transmitting type, as mentioned above. Consequently, the conventional sensor is such that a light-emitting device and a light-receiving device are disposed in opposed relation between the rotary shaft of the steering system and a housing, and a certain amount of space is required for these structural reasons. In addition, since the conventional steering sensor is already fabricated, there is little freedom available as far as mounting is concerned. This makes it very difficult to retrofit an existing vehicle with the sensor, and the sensor has little universality since it can be used only in specific vehicle models.
Another problem is that since the light-transmissive photosensor employs a pulse counting arrangement, it is not possible to sense the absolute steering angle prevailing when the ignition switch is turned on.